I still have the Sigma 17-70 and the Contemporary is not as sharp. This is not sold, but is on the 550D my girlfriend use. Speak the better magnification, the rum and 70mm above the lower weight of the Contemporary. If I had to choose between the two, I would probably pick up now 17-50. The image quality and the continuous 2.8-aperture are now times very strong arguments.
But beware: The first copy of the 17-50 was a real pickle! Violent fehlfokus on phase AF at moderate to high focal lengths, making the lens useless.
